Cancer can be treated with surgery, hormonal therapies, chemotherapies and/or radiotherapies but in many cases, cancers, which are often characterized by an advanced stage, cannot be cured with present therapeutics. Therefore, novel cancer cell targeted approaches such as gene therapies are needed.
During the last twenty years gene transfer technology has been under intensive examination. The aim of cancer gene therapies is to introduce a therapeutic gene into a tumor cell. These therapeutic genes introduced to a target cell may for example correct mutated genes, suppress active oncogenes or generate additional properties to the cell. Suitable exogenous therapeutic genes include but are not limited to immunotherapeutic, antiangiogenic, chemoprotective and “suicide” genes, and they can be introduced to a cell by utilizing modified virus vectors or non-viral methods including electroporation, gene gun and lipid or polymer coatings.
Requirements of optimal viral vectors include an efficient capability to find specific target cells and express the viral genome in the target cells. Furthermore, optimal vectors have to stay active in the target tissues or cells. All these properties of viral vectors have been developed during the last decades and for example retroviral, adenoviral and adeno-associated viral vectors have been widely studied in biomedicine.
To further improve tumor penetration and local amplification of the anti-tumor effect, selectively oncolytic agents, e.g. conditionally replicating adenoviruses, have been constructed. Oncolytic adenoviruses are a promising tool for treatment of cancers. Tumor cells are killed by oncolytic adenoviruses due to a replication of the virus in a tumor cell, the last phase of the replication resulting in a release of thousands of virions into the surrounding tumor tissues for effective tumor penetration and vascular re-infection. Tumor cells allow replication of the virus while normal cells are spared due to engineered changes in the virus genome, which prevent replication in non-tumor cells.
In addition to replication mediated cell killing, oncolytic adenoviruses can also be armed with different therapeutic transgenes. This approach combines the advantages of conventional gene delivery with the potency of replication competent agents. One goal of arming viruses is induction of an immune reaction towards the cells that allow virus replication. Virus replication alone, although immunogenic, is normally not enough to induce effective anti-tumor immunity. To strengthen induction of therapeutic immunity, viruses can be armed with stimulatory proteins such as cytokines for facilitation of the introduction of tumor antigens to antigen presenting cells such as dendritic cells, and their stimulation and/or maturation. Introduction of immunotherapeutic genes into tumor cells and furthermore, translation of the proteins, leads to activation of the immune response and efficient destruction of tumor cells. The most relevant immune cells in this regard are natural killer cells (NK) and cytotoxic CD8+ T-cells.
Adenoviruses are medium-sized (90-100 nm), nonenveloped icosahedral viruses, which have double stranded linear DNA of about 36 kilo base pairs in a protein capsid. The viral capsid has fiber structures, which participate in attachment of the virus to the target cell. First, the knob domain of the fiber protein binds to the receptor of the target cell (e.g. CD46 or coxsackievirus adenovirus receptor (CAR)), secondly, the virus interacts with an integrin molecule and thirdly, the virus is endocytosed into the target cell. Next, the viral genome is transported from endosomes into the nucleus and the replication machinery of the target cell is utilized also for viral purposes (Russell W. C. 2000, J General Virol 81, 2573-2604).
The adenoviral genome has early (E1-E4), intermediate (IX and IVa2) and late genes (L1-L5), which are transcribed in sequential order. Early gene products affect defense mechanisms, cell cycle and cellular metabolism of the host cell. Intermediate and late genes encode structural viral proteins for production of new virions (Wu and Nemerow, 2004, Trends Microbiol 12: 162-168; Russell W. C. 2000, J General Virol 81, 2573-2604; Volpers C. and Kochanek S. 2004, J Gene Med 6 suppl 1, S164-71; Kootstra N. A. and Verma I. M. 2003, Annu Rev Pharmacol Toxicol 43, 413-439).
More than 50 different serotypes of adenoviruses have been found in humans. Serotypes are classified into six subgroups A-F and different serotypes are known to be associated with different conditions i.e. respiratory diseases, conjunctivitis and gastroenteritis. Adenovirus serotype 5 (Ad5) is known to cause respiratory diseases and it is the most common serotype studied in the field of gene therapy. In the first Ad5 vectors E1 and/or E3 regions were deleted enabling insertion of foreign DNA to the vectors (Danthinne and Imperiale 2000). Furthermore, deletions of other regions as well as further mutations have provided extra properties to viral vectors. Indeed, various modifications of adenoviruses have been suggested for achieving efficient anti-tumor effects.
For example, patent EP1377671 B1 (Cell Genesys, Inc.) and application US2003/0104625 A1 (Cheng C. et al.) describe an oncolytic adenoviral vector encoding an immunotherapeutic protein granulocyte-macrophage colony-stimulating factor (GM-CSF). Also, publication EP1767642 A1 (Chengdu Kanghong Biotechnologies Co., Ltd.) points out oncolytic adenoviral vectors having improved effects on human immune response.
Still, more efficient and accurate gene transfer as well as increased specificity and sufficient tumor killing ability of gene therapies are warranted. Safety records of therapeutic vectors must also be excellent. The present invention provides a cancer therapeutic tool with these aforementioned properties by utilizing both oncolytic and immunotherapeutic properties of adenoviruses in a novel and inventive way.